improvements in clump logic - part 3 + 4

- part 3: new class clumpTemplate in py/utils.py
-> make it possible to create clump templates (python objects)

- part 4: new method replaceByClumps() in py/wrapper/yadeWrapper.cpp
-> replace spheres by clumps using a list of templates and a list of amounts

- small bug fix in calm() method: now clumps will also be calmed

- added new example script, that shows usage of clumpTemplate and replaceByClumps()

Thank you all for your help!